Adhesives play important roles in our daily life, including office supplies (e.g. tapes, super glues, hot glues, etc), structure construction materials (e.g. epoxy, acrylics, silicone, etc), manufacturing and assembly of commercial products, and high-end devices. Although there are a diverse range of adhesive materials available commercially, each is designed for a specific application and most of them are for one-time usage. More importantly, once the adhesive material is fabricated, the adhesion properties are fixed.
The ability to actively induce features and textures on surfaces has been of great interest for many potential applications, including stretchable electronics, microlens arrays, MicroElectroMechanical Systems (MEMS), tunable surface adhesion and friction, and robotics. In the last decade various methodologies have been investigated to spontaneously form self organized structures with controlled morphologies ranging from macro-, to micro-, to nanoscale, as well as on the theoretical aspects. One widely adopted simple and effective approach is based on internal buckling force equilibrium within materials by coating a hard thin layer (through metal deposition or surface oxidization) on top of a pre-strained bulk substrate (i.e., heated), such as poly(dimethylsiloxane) (PDMS), followed by release of the pre-strain. During release, the self-organized wrinkles are formed simultaneously and permanently without further continuous input of external force or energy. No matter what wrinkle patterns that may be generated when altering localized internal force equilibrium within materials, the fundamental pattern lies in the same, that is either 1-dimensional (1D) ripple structure or 2-dimensional (2D) so-called herringbone structure.
Despite these advances, there is a need in the art to form various wrinkle patterns with a tunable adhesive force.